1. Field of the Invention
This invention relates generally to furnaces of the traveling grate type wherein materials such as iron ore, and the like, are pelletized and/or sintered at elevated temperatures and, more particularly, to the minimizing of the air flow at the interface of the material and the sidewalls of the traveling grate and to the protecting of the sidewalls of the traveling grates of the furnace from severe temperature conditions during the processing of the material carried by the grates.
2. Prior Art
The individual pallet frames that make up the continuous traveling bed or heating or sintering bed of the traveling grate machines are fitted with steel or ductile iron side plates. These side plates are to provide a sidewall to retain a considerable thickness of the material that is to be sintered, dried or pelletized. These side plates are to be intricately cast and machined so that mating surfaces of the preceeding and trailing pallet side plate assemblies will prevent air leakage and consequent bypassing of the desired air flow through the material. However, the high temperatures and erosion encountered during the heating process, and particularly the adverse effect of the ignition furnace, tend to cause this carefully-machined seal or mating surface to be quickly and easily lost. The resulting warping, cracking, distortion and wear permits air to bypass through the openings in the vertical sidewalls. Energy is thus wasted and at some locations the material or the bed will be subjected to conditions different than other locations insofar as the heating, sintering, drying or calcining conditions are concerned.
Shields have been proposed to protect the side plates from the deleterious effects of temperature. These shields are usually expendable, so they can be replaced whenever they have deteriorated to the extent that they are no longer protecting the sidewalls. Typical shields are those described in U.S. Pat. Nos. 3,559,967 and 3,384,355.
As the moist, powdered or granular material heats, dries, fuses and/or melts, the volume of the material changes. The material tends to pull away from the sides of the grate and this creates a problem of improperly heating or sintering the material next to the sidewalls of the pallets. U.S. Pat. No. 3,824,071 proposes to solve this problem by having inwardly- and downwardly-sloping side plate members fastened along the vertical sidewall member. Such sloping side plate members also have openings for the passage of hot gases so as to promote the heating of the material in process adjacent to the sloping sidewall members. It is the expectation of U.S. Pat. No. 3,824,071 that, as the volume of the material being treated changes, the bed of material will move lower along the wall but, due to the slope of the wall, still maintain a material to wall contact.